This invention relates to a device for precisely angularly positioning a rotating device. Specifically, this invention is directed to a device capable of rapidly accessing any angle within 360.degree. and thereafter precisely addressing a extremely fine angle.
Many devices, particularly measuring devices require that an output wheel be precisely angularly positioned. For example, X-ray diffractometers require that the sample to be measured be rotated with extremely fine resolution. However, the devices used to provide such resolution have been less than completely satisfactory. Such angular output positioning devices have often times utilized finely toothed gears. However, no matter how finely toothed the gearing, a gear drive suffers from two positioning problems. These problems are known as backlash and coasting. Backlash refers to the problem that before a gear is driven by a driving gear, the driving gear must take up slack before the driven gear moves. Coasting refers to the fact that the driven gear may keep moving after the driving gear stops. Belt drive arrangements are too flexible and subject to vibration. These factors can create accuracy errors when rotational resolution as fine as an arc-second or less is required.
Another problem with devices used for fine angular micro-positioning is that while a device may be capable of fine micro-positioning, it may not be capable of rotating the output device through a full 360.degree.. Often a second, coarse drive mechanism is necessary. Clearly, a device capable of driving an output wheel through a full 360.degree. and thereafter micro-positioning same, is desirable. The present invention is directed to providing such a device.